In recent years, vehicles in which an engine is mounted are such that there has been an increase in vehicles for which an idling reduction system is employed, with an object of improving fuel efficiency and the like. An idling reduction system is a system whereby the engine is automatically stopped in a case in which engine output is unnecessary, such as a halt due to stopping at a traffic light or in a traffic jam, and the engine is automatically restarted by a starter when engine output becomes necessary because of a starting operation by a driver.
Starting of an engine using an existing starter is carried out only by starting driving, but starting of an engine in a vehicle for which an idling reduction system is employed is also carried out while driving, such as at a halt due to stopping at a traffic light or in a traffic jam. Because of this, starting of the engine is carried out in a state wherein power is being supplied from a battery to another vehicle-mounted electrical part (for example, a satellite navigation system, a car audio, or a car air conditioner). Therefore, an inrush current momentarily flows to the starter when the engine is started, because of which battery voltage is momentarily reduced noticeably, and the supply of power to another electrical part momentarily stops.
Also, owing to an idling reduction system being employed, requirements with respect to starter lifespan are increasing. Starter lifespan is mainly determined by brush abrasion. Commutation sparks generated when a brush and commutator slide together are a main factor in brush abrasion. Therefore, a multilayer brush in which a multiple of resistance members of differing electrical resistance values are provided is used with an object of restricting commutation sparks (for example, refer to PTL 1).